This invention relates to X-Y stages primarily for pattern generating apparatus, and in particular to a hydraulically driven stage which can be used in a vacuum.
X-Y stages are used in a variety of apparatus where it is necessary to move a support independently in two essentially orthogonal directions. One of the important applications of such apparatus is optical pattern generation in integrated circuit fabrication. For example, in Electron Beam Exposure Systems (EBES), masks for IC processing are generated by writing on resist-coated glass plates with an electron beam. To accomplish this, the plates must be moved continuously in a controlled manner beneath the beam, and a high degree of accuracy and speed is required for acceptable yield. In the past generation of apparatus, the writing field measured typically 4.times.4 inches so that stages driven by lead screw assemblies and the like were adequate. Present and future generations of apparatus require a capability of patterning a 6.times.6 inch field, which necessitates a speed and accuracy not easily achieved by the prior art mechanisms. In addition, electron beam exposure requires processing of the plates in a vacuum (typically at pressures less than 1.times.10.sup.-5 Torr) where lubricants cannot easily be used. Thus, prior art stages usually had the drive means external to the vacuum with motion of the support member provided by some connecting arm (see, e.g., U.S. Pat. No. 3,790,155 issued to Longamore). With the increased field area and velocity requirements previously mentioned, it would be more efficacious to provide a closer proximity and more direct mechanical coupling between the drive means and plate support. This necessitates placing such drive means within the vacuum chamber itself.
Other types of optical pattern generators, although not requiring a vacuum, could also make use of an X-Y stage which provides high speed and accuracy. For example, step and repeat cameras are used in IC processing to pattern photoresist layers on semiconductor wafers a chip at a time. Thus, positional accuracy and speed are primary requirements. In addition, although EBES apparatus are presently used primarily for making master masks, an X-Y stage of sufficient speed may permit such apparatus to be employed for processing semiconductor wafers directly.
It is therefore a primary object of the invention to provide an X-Y stage capable of high speed and accuracy in moving and positioning a supporting member. It is a further object of the invention to provide such a stage which can be used within a vacuum.